There are many situations in which an underground pipe carrying a fluid, a gas or a liquid, develops a leak, which leak must then be located and repaired. A good example is the case of water distribution pipes buried at a depth down to a few metres below ground. One common location method makes use of the fact that the leaking fluid often creates a noise, typically a hissing sound, which is conducted along the pipe as vibration. The sound is also transmitted through the ground. Although the sound is rapidly attenuated by the ground, it is possible to hear the sound with suitable highly sensitive ground microphones, and therefore ground microphones are often made available to field crews in the water industry as a means of identifying and locating leaks.
It is naturally desirable to locate the leak simply by listening to the sound at the ground surface. Crews do sometimes try to use a ground microphone for final fixing of the position of a leak by moving the microphone around and searching for the point at which the leak noise is loudest. Unfortunately, the sound levels can be grossly distorted by underground heterogenities, and can easily be confused or even swamped by other sound sources above ground. In general, then, ground microphones do not seem to be effective, mainly because background noise obscures the signal, and this has reduced their credibility with field crews. The invention deals with these types of problems encountered by water leak location teams by listening to the leak sound source from a multiplicity of different positions spaced all around the sound, listening either simultaneously or sequentially, and by then suitably combining and processing the received signals to provide the desired indication of the source's location.